Papers by Keyword: Multi-Stage Forming

Abstract: Adaptive thermal management is a prerequisite for multi-stage tailored forming of hybrid steel-aluminium blocks, as each section of material must remain within its forming temperature window and the joining zone must be protected from excessive thermal stress. This study defines a control-oriented process space for a combined induction heating and dual-fluid spray cooling concept developed in the Collaborative Research Center (SFB) 1153 “Tailored Forming.” A three-phase test program is applied: Phase A quantifies and evaluates the influence of air pressure p_air, water pressure p_w, and nozzle distance d on the cooling performance and the formation of an axial gradient using standardized regression coefficients. In phases B and C, a reference setting is applied to rotationally friction-welded 20MnCr5/EN AW-6082 blocks in a cold-start and preheated state, which are representative of multi-stage forming processes. The results show that p_air and p_w dominate both the cooling capacity and the formation of gradients, while d plays a subordinate role in the range investigated. The relationships remain qualitatively consistent for hybrid blanks and preheated conditions when the heating program is adapted to the aluminium and joining zone boundaries. The derived actuator ranking forms the basis for closed-loop temperature control in volatile, multi-stage tailored forming chains.

Abstract: In the multi-stage incremental forming of straight-wall parts based on the extrusion from the forward and reverse side of the sheet, different forming area zoning will have different effects on the part thickness. The larger the area of the sheet metal participating in forming is, the better the thickness distribution is. However, the forming area zoning can be adjusted by using the inclination angle α and the height H of the auxiliary zoning surface. Research results show that the forming area of the sheet metal participating the forming will increase and the thickness of the formed part will also increase with the inclination angle α decreases and with the height H increases.

Abstract: Progressive and transfer dies are used for forming of sheet metal parts in large quantities. For a given part, the design of progressive die sequence involves the selection of the number of forming stages as well as the determination of the punch and die dimensions at each stage. This design activity is largely experience-based and requires prototyping involving several trial and error operations. In some cases, empirical data and the experience based design procedure can be combined with Finite Element Method (FEM) based analysis to reduce time and cost. Often, when using FEM in progressive die design, friction and its effect upon temperatures is not adequately considered. However, at each forming station the plastic deformation and the tribological conditions influence the material flow as well as the temperatures and pressures at the tool/workpiece interface. The performance of the lubricant and coolant, used in progressive die forming, is affected significantly by interface pressure and temperatures. Therefore, a progressive process and die design methodology should include the consideration of metal flow as well as temperatures and pressures. Heat transfer coefficient, friction, plastic deformation, forming speed at each forming stage, time for part transfer from one stage to the next, and the ability of the used lubricant to cool the dies, have considerable effect upon a successful stamping. This paper describes a method for designing a progressive die sequence for forming axisymmetric sheet metal parts. The methodology for process sequence design combines experience based empirical data obtained through previous designs, design rules and numerical simulations including plastic deformation and friction. The initial experience-based design was refined using FEM and the thinning of the material in each successive drawing stage was calculated. The thermo-mechanical model was obtained using a constant friction coefficient along the tool/workpiece contact zone. Finally, the tool/workpiece interface temperature and the normal pressures were estimated in order that the lubricant can be selected based on these process conditions. The design predictions, made by using empirical data and FEM, were compared with experimental data.

Abstract: In order to the difficult forming sheet metal part with the vertical wall to be formed by the multi-stage incremental forming, the algorithm of the recognition and modify the difficult forming surface of the vertical wall is studied. The method for generation of the technological model for multi-stage incremental forming is also presented. The case studies show that the algorithm is feasibility.

Abstract: The steel wheel centre discs are usually stamped by multi-stage sheet metal forming. The stage number and the content of every stage decide if the structure-pieces can be formed successfully and the final forming quality. In this paper, the forming characteristics of wheel centre disc were analyzed firstly and the reasonable two-stage stamping scheme of drawing and inverse-drawing are adopted. The numerical simulations of multi-stage stamping process are performed and connected together through deformation transmission. By means of FLD and changes of sheet metal chickness, the formability is analyzed and the forming process is optimized. The feasibility of multi-stage forming process simulation and the validity of the optimized scheme were verified by stamping in practice.

Abstract: This paper aims at presenting an experimental investigation to obtain the optimum formability of light-weight alloys under the multi-stage forming process. Titanium alloy sheets (Ti-6Al-4V) and aluminium alloy sheets (AA5052) are selected as forming specimens. The special fixture with heating device is applied in order to carry out the prestraining process. The swift forming test at warm-forming condition is performed for measuring the limit dome heights after the multi-stage formign process. The outcomes of this investigation are valuable for engineers to design and fabricate high-quality light-weight components efficiently.

Abstract: The wall thickness around an inner corner in 3-stages formed cups with a flange was increased by means of conical punches in the 1st and 2nd stages. Since the strength of the formed cups is greatly improved by the increase in wall thickness, the weight of the formed products is reduced by an optimum distribution obtained from the increase in wall thickness. The increase in thickness around the inner corner is obtained by compressing the side wall and conical bottom of the cup in the 3rd stage. As the punch angle increases, the increase in thickness at the inner corner becomes large. The amount of compression is expressed by a drawn volume after the 2nd stage. A maximum 9% increase in wall thickness around the inner corner was successfully obtained for the punch angle of 25º.